Constituent parts of an automatic transmission of a vehicle include a planetary gear element formed by rotation elements such as a sun gear, a ring gear and a planetary gear, and friction engagement elements. In such an automatic transmission, any of a plurality of gears is implemented by switching a transmission channel of torque transmitted from an engine by switching a combination between the friction engagement elements to be engaged. Particularly, in an automatic transmission having a number of gears (such as a six-gear automatic transmission), a plurality. of clutch elements serving as input elements and a plurality of brake elements serving as reaction elements are provided.
In such an automatic transmission, in a case where a shift is performed over gears having plural gears inbetween by a shift operation, an acceleration demand or the like, both the input elements and the reaction elements may be switched so as to perform the shift. In this case, after an intermediate gear is implemented by switching one of the input elements and the reaction elements, the other are switched so that the shift is performed.
Such shift control of performing switchover in two steps via the intermediate gear is already known. For example, W02003/029699 discloses a shift control apparatus for an automatic transmission capable of quickly responding to a demand and smoothly achieving dual switchover control, even in a case where a driver changes a shift intention and requests another gear at the time of a shift to be achieved by a plurality of switchover control operations, after the change in a target gear is inhibited. This shift control apparatus is a shift control apparatus for an automatic transmission provided with shift control means for achieving a plurality of forward gears by engagement and disengagement control on a plurality of friction elements relating to a shift of the automatic transmission. The shift control apparatus is characterized by including dual switchover shift determining means for determining a shift from a Nth gear achieved by bringing a first friction element and a second friction element at least into an engaged state, to a (N-α)th gear achieved by bringing at least the first friction element and the second friction element into a disengaged state and engaging a third friction element and a fourth friction element having at least one intermediate gear between the Nth gear and the (N-α)th gear achieved by engaging the second friction element and the third friction element; jump shift control means for achieving the shift from the Nth gear to the (N-α)th gear by disengaging the first friction element and engaging the fourth friction element at least at the time of determination of dual switchover shift, lowering engagement force of the second friction element before a gear ratio reaches a gear ratio corresponding to the intermediate gear, and disengaging the second friction element and engaging the third friction element at least after passage of the gear ratio through the gear ratio corresponding to the intermediate gear; target gear ratio change inhibiting means for determining to inhibit the target gear from being changed from the (N-α)th gear at predetermined timing after start of the shift from the Nth gear to the (N-α)th gear until an end of the shift control; and target gear ratio change permitting means for rechecking the shift intention of the driver when the gear ratio reaches the gear ratio corresponding to the intermediate gear, and permitting the gear of the target gear ratio from being changed to a gear corresponding to the intention of the driver when the gear of the target gear ratio differs from the (N-α)th gear, even if the change in the gear of the target gear ratio is inhibited.
According to the shift control apparatus for the automatic transmission disclosed in the above patent literature, when the driver intends to change the gear, it is possible to achieve the shift for a short time. When the driver does not intend to change the gear, oil pressure of an H/C is lowered before reaching a gear ratio corresponding to a fifth gear. Therefore, the shift is not settled and there is no generation of a plurality of shift shock in the duel switchover. Thereby, it is possible to achieve a smooth duel switchover shift.
In the shift control apparatus disclosed in the above patent literature, when the gear ratio reaches the gear ratio corresponding to the intermediate gear, the shift to the target gear is inhibited in accordance with the shift intention of the driver at the time of a shift over the gears having plural gears inbetween. However, in a case where there is no change in the intention of the driver, control of changing to the target gear is performed after implementing the intermediate gear. That is, the switchover from the second friction element to the third friction element is performed after performing the switchover from the first friction element to the fourth friction element so that the intermediate gear is completely implemented. Therefore, a time period of a shift action may be elongated.
Alternatively, in a case where the switchover of the first friction element and the second friction element is performed in parallel, there is a rotation element with the revolution speed not detected in the automatic transmission until engagement of the third friction element and engagement of the fourth friction element after disengagement of the first friction element and disengagement of the second friction element. Therefore, the shift shock may be generated at a time point when the third friction element and the fourth friction element are engaged.